Ditto, you don't have to have a X pipe. They are not really necessary for engines under 350 HP. However, since you are dropping a 475 HP engine in, you probably should have one and from what I read it would have a definate benifit to your HP delivery to the wheels.
The objective of a X pipe is to increase flow by reducing the effect of muffler restriction. By having a X pipe, exhaust flows better because the effective restriction of a muffler is cut in 1/2. The effect of this is to deliver more horsepower to the wheels. Since flow is one of the most important things in a performance engine, the larger the engine the more necessary the X pipe becomes. So basically you want to reduce as much back pressure as possible. That also means keeping bends to the minimum.
As far as the transfer case is concerned, you have two choices:
1. The least desirable for exhaust flow reasons is bringing both pipes down the right side of the truck and then after clearing the transfer case take the left pipe either back with the right pipe and exit both at the same location or take the left pipe back over to the left side to exit. The advantage of this is that a close X pipe can be done when the pipes are right next to eachother.
OR
2. Put atleast a 4" body lift on the truck and then the left pipe will be able to go strait back to the rear. Check out Freaks system.
Good luck,

>-